This invention relates to a communication system enabling N people to use a switching system such as a private branch exchange for 1.times.N communication (N being an integer greater than two).
The modern private branch exchange is a digital electronic device comprising a time-division switch and a central controller. The central controller can be programmed to implement a variety of services besides what is technically referred to as "plain old telephone service" (POTS). One of these additional services is a 1.times.N communication service known, for example, as announcement or broadcast service. This service can be utilized for communication among employees of a department store, hotel, hospital, or other organization.
A prior-art 1.times.N communication scheme employs standard extension telephone sets coupled to a private branch exchange, either by wires or by wireless links. Information designating N of these extension telephone sets as a broadcast group is stored in a memory of the central controller. When a person at one of these N extension telephone sets wishes to make an announcement to the people in the broadcast group, he picks up the handset and performs a series of special operations, such as momentarily depressing the hook switch then dialing a special service code. The central controller responds by setting up a circuit in the private branch exchange that allows the person's voice to be heard at the rest of the N extension telephone sets in the group. At the end of the announcement, the person performs another special operation to release the circuit. If another person at one of the N extension telephone sets wants to reply to the announcement, he can do so by a similar series of operations.
One disadvantage of this prior-art scheme is that the numerous special operations required make it difficult and inconvenient to use. Each time a person wishes to speak, for instance, he must enter a special service code.
Another disadvantage is that the central controller must execute a special service program each time the service code is entered. This extra load reduces the ability of the private branch exchange to handle normal telephone traffic, leading to problems such as long call setup delays.